This invention relates to semiconductor junction lasers.
The stripe-geometry contact for junction lasers was proposed by R. A. Furnanage et al. (U.S. Pat. No. 3,363,195, granted Jan. 9, 1968) more than a decade ago and has been incorporated, in one form or another, in various heterostructure laser configurations in use and under study today. These lasers, which range from the simple double heterostructure (DH) (I. Hayashi, U.S. Pat. No. 3,758,875, granted Sept. 11, 1973) to more complicated buried heterostructures (BH) [T. Tsukada, Journal of Applied Physics, Vol. 45, p. 4899 (1974)], each have one or more advantageous operating characteristics.
The DH laser has the longest lifetime of all semiconductor lasers, exceeding 10.sup.5 hours to date, and is characterized by low thresholds and fundamental transverse mode operation. On the other hand, it has a wide beam divergence, a nonlinearity (known as a "kink") in its light-current (L-I) characteristic, and incomplete lateral current confinement.
The Tsukada BH laser, which includes a GaAs active region completely surrounded by Al.sub.0.3 Ga.sub.0.7 As, has effective transverse mode stabilization, but the refractive index change along the junction plane is so large that stable fundamental mode lasing is possible only for active layer widths of .ltoreq.1 .mu.m, resulting in low output power (e.g., 1 mW) and large beam divergence in both transverse directions. In BH lasers with wider active layers, higher order modes are easily excited near threshold.